The present invention relates to a brake adjustment method and apparatus thereof for making a steering brake adjustment to ensure proper steering brake performance in a tracklaying vehicle in which a right or left turn is made by controlling clutch hydraulic pressure and brake hydraulic pressure through operation of an electrical power-assisted steering lever.
In a known tracklaying vehicle such as bulldozers, the clutch and brake attached to each of the right and left drive wheels are controlled to effect right and left turns of the vehicle. More specifically, if the steering lever is operated in either the right or left steering direction during traveling of the vehicle, the clutch on the side toward which the steering lever has been operated is released from its engaged state, while the brake on the same side is actuated in the braking direction with the crawler belt only on this side being brought to a stop, so that the vehicle turns in the desired direction.
The so-called electronically controlled steering systems come into common use for providing clutch and brake control. Such a steering system includes (i) an electrical power-assisted steering lever, (ii) a steering command signal generator for issuing a steering command signal in accordance with the operating amount of the steering lever and (iii) an electronic proportional control valve controlled based on the output from the steering command signal generator, and controls the clutches and brakes through control of the electronic proportional control valve.
The electronically controlled steering systems present the bothersome drawback that if variations in vehicle performance occur owing to variations in the constituents (e.g., solenoids and springs) of the control valves or variations in the thickness of the clutch disks or brake disks, mechanical adjustments (e.g., shim adjustment and stroke adjustment) have to be carried out as required whenever they occur. These steering systems suffer from another problem that long use of the vehicle leads to wear etc. of the operation system including the steering brakes and steering clutches, resulting in degradation of vehicle performance.
For constantly providing desired proper steering brake or steering clutch performance to overcome the forgoing problems, it is necessary to incorporate a system which enables a brake or clutch adjustment at the time of delivery or check of a vehicle.
There is known a steering brake adjustment method carried out in the following procedure.
Step 1: A crawler belt is lifted from the ground by use of implements (blade and ripper) or jacks.
Step 2: Engine rotation is set to a low idling state.
Step 3: An adjustment mode is set.
Step 4: The crawler belt is rotated with the transmission placed in the third forward speed range (F3).
Step 5: The test starting switch is turned on. At that time, a test current flows to the brake solenoid for a specified period of time and after the elapse of the specified time, the speed of the crawler belt returns to a normal speed.
Step 6: The adjuster makes a check as to whether or not the crawler belt had stopped before the speed of the crawler belt returned to the normal speed. Then, if it is determined the crawler belt had stopped, the adjuster makes a check again with an increased setting of hydraulic pressure to determine whether the crawler belt stops.
Step 7: If the crawler belt did not stop before returning to the normal speed, the adjuster makes a check again with a decreased setting of hydraulic pressure to determine whether the crawler belt stops. Checks are made in this way and when the crawler belt has stopped, the adjustment mode is ended.
A prior art technique associated with the invention is disclosed in Japanese Patent Publication (KOKAI) Gazette No. 8-214676 (1996). This technique is associated with a steering brake pressure control system such as combines in which an adjustment for the interrelationship between the reference property values of steering brake pressure on the steering lever side and steering brake pressure on the pedal side is made such that the initial value of either one of the reference values is adjusted and altered, thereby automatically adjusting/altering the initial value of the other reference value.
The known adjustment method implemented through the above-described steps 1 to 7, however, has revealed the disadvantage that since brake hydraulic pressure is gradually decreased while a crawler belt being rotated with the vehicle lifted and an adjustment is made based on the instance of a stop of the crawler belt which has been confirmed by the adjuster by visual inspection of the movement of the crawler belt, the adjuster has to judge the switch point at which the kinematic friction is switched to static friction, which leads to considerable variations in detection properties. In addition, the interventional judgement by the adjuster would be accompanied with variations when different adjusters make the judgement. Finally, since the vehicle needs to be lifted during the adjustment, a jack is required for lifting it. Even if the vehicle is lifted by an implement attachable to the front or rear part of the vehicle, the adjustment has to be disadvantageously carried out with the implement mounted on the vehicle.
The prior art associated with the present invention, which is disclosed in Japanese Patent Publication No. 8-214676, is intended to provide control for interlinking the steering pressure adjustments on the steering lever side and on the pedal side, but principally differs from the subject of the invention which is primarily made for providing a steering brake adjustment method.
The invention is directed to overcoming the foregoing problems and a primary object of the invention is therefore to provide a brake adjustment method and apparatus thereof, which make it possible to readily and accurately provide proper brake hydraulic pressure compensation without variations due to different adjusters and without a need for lifting the vehicle.
The above object can be achieved by a brake adjustment method according to a first aspect of the invention. The method is adapted for use with a tracklaying vehicle wherein right and left drive wheels are each provided with a clutch and a brake and wherein clutch hydraulic pressure and brake hydraulic pressure are controlled by operation of an electrical power-assisted steering lever to allow a right or left turn of the vehicle,
the method being made such that when an adjustment mode is selected with the vehicle in its stopped state, a command value for the brake hydraulic pressure at the start of vehicle traveling is detected while the brake hydraulic pressure being gradually changed, and an adjustment for a brake is made based on the detected command value.
According to the invention, for brake adjustment, the adjustment mode is set with the vehicle in its stopped state and brake hydraulic pressure is gradually varied (e.g., increasing) during the adjustment mode. Then, a command value of brake hydraulic pressure at the start of vehicle traveling is detected and according to this command value, a brake adjustment is carried out. With this arrangement, variations due to different adjusters can be avoided, and variations in detection properties can be eliminated and an easy, accurate brake adjustment can be made thanks to the adjustment using the switch point, as the judgement basis, at which static friction is switched to kinematic friction. In addition, since there is no need to rotate the crawler belt with the vehicle lifted during the adjustment, a jack for lifting the vehicle is no longer required. Further, the adjustment operation can be carried out with no implements mounted on the vehicle. Finally, since it is not necessary to keep the brake in its sliding state for a long time, heat does not develop in the brake, which obviates the risk of adverse effects on the brake.
According to a second aspect of the invention, there is provided a brake adjustment apparatus adapted for use with a tracklaying vehicle wherein right and left drive wheels are each provided with a clutch and a brake and wherein clutch hydraulic pressure and brake hydraulic pressure are controlled by operation of an electrical power-assisted steering lever to allow a right or left turn of the vehicle, the apparatus comprising, as shown in the general block diagram of FIG. 1,
(a) adjustment mode setting means 1 for setting an adjustment mode for adjusting the brake hydraulic pressure to a proper value, while the vehicle being in its stopped state;
(b) brake hydraulic pressure changing means 2 for controlling the brake hydraulic pressure to gradually change when the adjustment mode has been set by the adjustment mode setting means 1;
(c) vehicle travel start detecting means 3 for detecting a start of traveling of the vehicle;
(d) brake pressure command value detecting means 4 for detecting a brake pressure command value at the start of traveling of the vehicle, if a start of vehicle traveling is detected by the vehicle travel start detecting means 3 while the brake hydraulic pressure being gradually changed by the brake hydraulic pressure changing means 2; and
(e) brake hydraulic pressure correcting means 5 for correcting the brake hydraulic pressure to a proper value, based on the brake pressure command value detected by the brake pressure command value detecting means 4.
The second aspect of the invention is associated with an apparatus which implements the brake adjustment method of the first aspect. For starting brake adjustment, the adjustment mode is set by the adjustment mode setting means 1 while the vehicle is in its stopped state. In this adjustment mode, the brake hydraulic pressure is gradually changed (e.g., increasing) by the brake hydraulic pressure changing means 2. If a start of traveling of the vehicle is detected by the vehicle travel start detecting means 3 during the changing of the brake hydraulic pressure, a command value of brake hydraulic pressure at the start of traveling of the vehicle is detected by the brake pressure command value detecting means 4 and based on the detected command value, the brake hydraulic pressure correcting means 5 corrects the brake hydraulic pressure so as to have a proper value. This arrangement provides the same effect as in the first aspect of the invention and is particularly advantageous in that since the travel starting condition of the vehicle is automatically detected by the vehicle travel start detecting means 3, variations attributable to different adjusters can be avoided so that anybody can make an adjustment with ease.
Preferably, the apparatus of the second aspect of the invention is modified such that the adjustment mode setting means 1 can set the adjustment mode with at least one of the clutches, which is located on an adjusted side, being in its engaged condition at all times, and such that a transmission output-side rotation sensor for detecting the rotation of the output side of the transmission of the vehicle is used as the vehicle travel start detecting means 3. In such an adjustment mode, at least one of the clutches, which is located on an adjusted side, is in its engaged state at all times, and therefore, when the brake slips during the adjustment mode, in other words, when the vehicle starts traveling, the vehicle travels straight-ahead so that a safer brake adjustment can be effected. By use of a transmission output-side rotation sensor as the vehicle travel start detecting means 3, the sliding condition of the brake can be readily and accurately detected.
The second aspect is preferably modified such that the brake hydraulic pressure changing means 2 sets an initial value for the brake hydraulic pressure in accordance with a reference line representing reference brake pressure command values relative to the tractive force of the vehicle, the initial value being used as a basis for changing the brake hydraulic pressure. This makes it possible to determine a proper brake hydraulic pressure command value based on the tractive force so that a brake hydraulic pressure closer to the hydraulic pressure at the time of brake sliding can be effectively obtained, without being affected by variations in other parts (e.g., engine and power line) than the steering section.
It is preferable, in this case, that the brake hydraulic pressure changing means 2 controls the brake hydraulic pressure so as to increase step-wise by a specified amount at specified time intervals, starting from the above initial value. By virtue of this arrangement, the brake hydraulic pressure at the start of sliding of the brake can be readily and accurately obtained.
The apparatus according to the invention may be modified such that the brake hydraulic pressure correcting means 5 corrects the brake hydraulic pressure based on the difference between a reference brake pressure command value corresponding to a specified tractive force of the vehicle and the brake pressure command value detected by the brake pressure command value detecting means. This makes it possible to easily obtain a brake hydraulic pressure value to be corrected.